Install @babel/preset-react for non-SWC generator installs

[justin808]

Summary

• Add BABEL_REACT_DEPENDENCIES to the generator dependency manager
• Install @babel/preset-react as a dev dependency when SWC is not the active transpiler
• Keep SWC path unchanged (no Babel preset installed when SWC is used)
• Extend generator specs to verify:
  • Babel preset is included for non-SWC setups
  • Babel preset is skipped for SWC setups
  • install generator output includes @babel/preset-react for older Shakapacker/Babel defaults

Closes #2281

Test plan

• Proposed fix (UNTESTED in this environment)
• Intended Ruby checks:
  • bundle exec rspec react_on_rails/spec/react_on_rails/generators/js_dependency_manager_spec.rb
  • bundle exec rspec react_on_rails/spec/react_on_rails/generators/install_generator_spec.rb
• Blocked by local Ruby version (2.6.10) vs project requirement (>= 3.0.0)

Summary by CodeRabbit

• New Features

  • Dependency management now installs the Babel React preset when the SWC transpiler is not active, with user-facing warnings and fallback instructions if installation fails.

• Tests

  • Expanded test coverage to verify conditional Babel React installation, warning behavior, and absence when SWC is used.

[coderabbitai]

Walkthrough

The generator now installs @babel/preset-react for non-SWC setups by adding a new constant and code path that conditionally adds the Babel React preset when SWC is not the active transpiler.

Changes

Cohort / File(s)	Summary
Core Dependency Manager Implementation react_on_rails/lib/generators/react_on_rails/js_dependency_manager.rb	Added BABEL_REACT_DEPENDENCIES constant and a private add_babel_react_dependencies path; changed control flow to install Babel React preset only when SWC is not used.
Generator Integration Test react_on_rails/spec/react_on_rails/generators/install_generator_spec.rb	Updated test to expect @babel/preset-react in devDependencies for older Shakapacker (non-SWC) cases.
Dependency Manager Unit Tests react_on_rails/spec/react_on_rails/generators/js_dependency_manager_spec.rb	Adjusted test double signature for add_npm_dependencies, added assertions for BABEL_REACT_DEPENDENCIES, and expanded tests for the new Babel-specific add path and its warning/error behavior.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐇 I hopped through packages, sniffed the stack so neat,
Found Babel's missing preset and made the fix complete,
When SWC skips JSX, now @babel/preset-react lands,
No broken builds, just tidy rails and happy hands. ✨📦

🚥 Pre-merge checks | ✅ 5 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 14.29% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: installing @babel/preset-react for non-SWC generator configurations, which aligns with the core objective in the PR.
Linked Issues check	✅ Passed	The PR successfully implements all coding requirements from issue #2281: adds BABEL_REACT_DEPENDENCIES constant, conditionally installs @babel/preset-react for non-SWC configs, skips it for SWC, and extends specs to verify both paths.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the issue objective: dependency manager updates, new Babel preset handling logic, and test coverage for both SWC and non-SWC scenarios without extraneous modifications.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into master

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch codex/fix-2281-babel-preset-react-dep

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[greptile-apps]

Greptile Summary

This PR fixes a missing dependency issue where the generator creates a babel.config.js file that requires @babel/preset-react, but wasn't installing it for non-SWC setups.

Key Changes:

• Adds BABEL_REACT_DEPENDENCIES constant containing @babel/preset-react
• Creates new add_babel_react_dependencies method following the existing error handling pattern
• Updates add_js_dependencies to conditionally install either SWC dependencies OR Babel preset based on using_swc? check
• Extends test coverage to verify the preset is installed for Babel setups and skipped for SWC setups
• Adds add_npm_dependencies_calls tracking to test mock for better assertion capabilities

Why This Matters:
The generated babel.config.js template references @babel/preset-react on line 11, which would cause build failures if the package isn't installed. This fix ensures the dependency is present when needed.

Confidence Score: 5/5

• This PR is safe to merge with no identified risks
• The implementation follows established patterns in the codebase, includes comprehensive test coverage, and addresses a legitimate bug where generated files would reference missing dependencies. The conditional logic properly handles both SWC and Babel paths without breaking existing functionality.
• No files require special attention

Important Files Changed

Filename	Overview
react_on_rails/lib/generators/react_on_rails/js_dependency_manager.rb	Adds BABEL_REACT_DEPENDENCIES constant and add_babel_react_dependencies method, installs @babel/preset-react for non-SWC setups
react_on_rails/spec/react_on_rails/generators/install_generator_spec.rb	Adds test assertion to verify @babel/preset-react is installed for older Shakapacker/Babel configurations
react_on_rails/spec/react_on_rails/generators/js_dependency_manager_spec.rb	Adds comprehensive tests for BABEL_REACT_DEPENDENCIES, add_babel_react_dependencies, and conditional Babel preset installation logic

Flowchart

flowchart TD
    A[Generator starts] --> B[add_js_dependencies called]
    B --> C{using_swc?}
    C -->|true| D[add_swc_dependencies]
    C -->|false| E[add_babel_react_dependencies]
    D --> F[Install @swc/core and swc-loader as devDependencies]
    E --> G[Install @babel/preset-react as devDependency]
    F --> H[Continue with other dependencies]
    G --> H
    H --> I[babel.config.js template requires @babel/preset-react]
    I --> J{SWC path?}
    J -->|Yes| K[No babel.config.js needed - SWC handles transpilation]
    J -->|No| L[babel.config.js uses @babel/preset-react preset]

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_{Last reviewed commit: ff49925}